Method and apparatus for the production of gaseous ammonia from a urea solution

ABSTRACT

A safe, economical and predictable apparatus for producing ammonia from a urea solution, preferably where only a small amount of ammonia is required, (i.e. for SCR denitrification for small boilers, flue gas conditioning to enhance precipitator efficiency and/or alleviate plume problems, SNCR and the like), using an ultrasonic processor to cause “cold boiling” of portions of such solution and produce gaseous ammonia.

RELATED APPLICATIONS

This application is a Division of U.S. application Ser. No. 11/893,306,filed Aug. 15, 2007. which in turn is a Division of U.S. applicationSer. No. 11/027,972, filed Dec. 30, 2004.

BACKGROUND OF THE INVENTION

Ammonia is an extremely important chemical which has innumerable uses ina wide range of areas, for example: process, industry and utility uses.The instant invention is concerned with a method and means to safelyproduce relatively small amounts (i.e. up to 150 pounds per hour, andperhaps up to 300 pounds per hour) of ammonia from urea, for such uses.

Areas of use for such relatively small quantities of ammonia are quitevaried and, for purposes of this discussion, such areas include, but arenot limited to: providing ammonia equipment and processes, of the typeillustrated in U.S. Pat. No. 2,356,717, to help increase the efficiencyof an electrostatic precipitator to remove flyash from the flue gasstream of a fossil fuel burning boiler; to alleviate “blue plume”problems when burning a high sulfur content oil in a boiler such asillustrated in U.S. Pat. No. 5,024,171; and to remove the NOxcontaminants contained in a flue gas stream of energy producing boilersor combined cycle systems, in conjunction with selective catalyticreduction (SCR), and/or selective non-catalytic reduction (SNCR),systems (see U.S. Pat. Nos. 4,124,536 and 3,900,554, respectively).

Ammonia for uses such as described above, is often delivered in the formof anhydrous ammonia, or aqueous ammonia. Anhydrous ammonia is used inmassive quantities world-wide for many industrial and agriculturalpurposes. Anhydrous ammonia is gas at ambient temperatures andpressures, and is normally shipped and stored as a liquid, either inpressure vessels at ambient temperature, and high pressure (i.e. over 16bars), or in refrigerated vessels at ambient or nearly ambient pressure,and at about −33° C. It is transported in bulk in ships, barges, andrailroad tank cars, and in tank trucks on public roads and highways and,in instances of relatively small usage per hour, such as envisioned withthe present invention, perhaps in high pressure cylinders. It isfrequently used and stored at industrial sites in populated areas. It isnow coming into wider use for the removal of NOx from flue gas at powergenerating stations, industrial heaters, or in combined cycle systems,in urban areas.

Anhydrous ammonia is an extremely hazardous, toxic, and volatilematerial. In the event of an accidental discharge, it can causeimmediate death or injury to humans and animals and rapid death to treesand plants. Both anhydrous liquid ammonia, and concentrated aqueousliquid ammonia, display a deadly characteristic which substantiallyincreases the risk of widespread injury and death in case of a spill.Specifically, upon sudden release to the atmosphere, as might occur in asudden and accidental discharge, the ammonia can form a cloud producedof an aerosol fog of liquid ammonia droplets. Unlike gaseous ammonia,which, though toxic, is lighter than air and quickly dissipates toharmless concentrations, the cloud can persist for a surprisingly longtime, as long as several hours, before it finally disappears. The cloudis typically heavier than air and tends to drift along the surface ofthe earth, i.e., the ground or the surface of a body of water. The cloudmoves with the wind and can sweep over a total area, i.e., a“footprint,” much larger than the area covered by the cloud at any onemoment. Contact with the cloud may be instantly incapacitating, and asingle breath can be fatal.

In addition to the inherent danger of storing, transporting and handlinglarge quantities of ammonia, the expense insofar as safety aspects,insurance costs, specialized training, and the difficult to quantifyemotional exposure of living and/or working next to a such potentialcatastrophe, it is apparent that if another, less hazardous commoditycould be transported or stored instead of ammonia, and then be readilyconverted to ammonia, the hazards associated with ammonia shipment andhandling would be considerably reduced. To some extent, attempts havebeen made in the supply of ammonia for NOx control in power plant andindustrial environments by substituting concentrated aqueous liquidammonia for anhydrous ammonia. Such a solution has achieved only limitedsuccess, due to any number of factors, for example: the high energy costof transporting and vaporizing the water carrier, relatively costlystorage facilities; and, even though aqueous ammonia is safer to handlethan anhydrous ammonia, it is still difficult and costly to handle in asafe manner.

Urea is an ideal candidate as an ammonia substitute. Urea is a non-toxicchemical compound and, for purposes of this discussion, presentsessentially no danger to the environment, animals, plant life and humanbeings. It is solid under ambient temperatures and pressures.Consequently, urea can be safely and inexpensively shipped in bulk andstored for long periods of time until it is converted into ammonia. Itwill not leak, explode, be a source of toxic fumes, requirepressurization, increase insurance premiums, require extensive safetyprograms, or be a concern to the plant, community and individuals whomay be aware of the transportation and/or storage dangers of ammonia.Further, urea can be used to produce gaseous ammonia:

-   -   on-site    -   on-demand    -   with rapid response time    -   with maximum turn down availability    -   with utmost safety    -   with significant economies    -   with automatic operation    -   with low maintenance

The use of urea with the advantages discussed hereinabove wererecognized by Applicant heretofore, as illustrated, described andclaimed in his U.S. Pat. No. 6,093,380. In addition to the systemdescribed in the '380 patent, another commercially available systemwhich also produces ammonia form a urea feed stock is shown in U.S. Pat.No. 6,077,491 The prior art systems mentioned in this paragraph havebeen used primarily for fulfilling relatively larger ammoniarequirements and, as such, are not necessarily the most appropriatedesign for small ammonia production requirements. For example—cost,unnecessarily high pressure and temperature requirements, specialtymetals, physical and chemical scale down problems, load followingrequirements, expensive or ineffective controls for such small ammoniaproduction requirements, and the like.

SUMMARY OF THE INVENTION

By means of the present invention which starts with a solutionized ureafeed stock, and uses an ultrasonic generator in accordance with theapplied principles of sonochemistry to produce NH₃ and CO₂ (i.e.(NH₂)₂CO+H₂O→2NH₃+CO₂) on site and on demand, the hereinabove mentioneddeficiencies of prior art systems are overcome or, in the least, greatlyalleviated, for the production of small quantities of ammonia for use indownstream processes. In particular, the ammonia production systems ofthe present invention operates as follows:

-   -   1. Solutionized urea is obtained from a suitable source;    -   2. The solutionized urea is passed through, or in the vicinity        of, ultrasonic waves produced by an ultrasonic transducer or the        like, to produce a powerful sonic field in the solutionized        urea. The frequency of the ultrasonic field is in the range of        15 to 100 kHz, preferably in the range of 20 to 40 kHz.    -   3. Applying the ultrasonic field to the solutionized urea        results in ultrasonic processing, which is the blasting of        liquids with the very intense sound of high frequency producing        very good mixing and powerful chemical and physical reactions.        More specifically, sonochemistry is the result of acoustic        cavitation, the formation, growth and implosive collapse of        bubbles in a liquid. The collapse of such bubbles creates hot        spots with temperatures as high as 5000° C., pressures up to 800        bar. These conditions are responsible for a variety of chemical        and physical effects. For example, volatile precursors have been        sonochemically decomposed into nanostructured materials with        unique morphology and catalytic activity. In the instant        situation of applying ultrasonic waves to the solutionized urea,        ammonia and carbon dioxide are generated by the transitory high        temperature and pressure hydrolysis process, and released from        the solution. Some of this ammonia and carbon dioxide is in the        form of free gas and other of such is locked in solution. It is        to be noted that these high pressures and temperatures only        occur for milliseconds and do not effect the temperature and        pressure of the working fluid, which is generally maintained in        the range of 80 to 150° C. and 1-5 bar (preferably 1.2-3 bar).    -   4. To free the gas locked in solution, the flow is then sparged        (i.e. by steam or other physical agitation). In all instances        heat is applied to the solution to maintain it at or near its        boiling point.

As can be readily appreciated, a system, such as described above, forthe conversion of urea to ammonia on site and on demand: will obviatethe need for high pressure and/or high temperature; only a relativelysmall chamber for process requirements is necessary; is highlycontrollable (i.e. both the intensity of the ultrasonics and thesparging fluid); is relatively inexpensive; only requires moderatecontrols; there is no need for specialized materials; and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a fossil fuel burning powerplant which incorporates the principles of the present invention;

FIG. 2 is a schematic representation of an on-site, on-demand urea toammonia system constructed in accordance with the principles of thepresent invention, and which is of the type incorporating immersibletransducers;

FIG. 3 is a schematic representation of a plan view (with top plateremoved for clarity) of an on-site, on-demand urea to ammonia systemconstructed in accordance with the principles of the present invention,and which is of the type incorporating a parallel transducers array anda defined flow channel for the urea solution; and

FIG. 4 is a side elevational view of the urea to ammonia systemillustrated in FIG. 3

FIG. 5 is a schematic representation of an on demand urea to ammoniasystem such as shown in FIGS. 3 & 4, with the primary distinctiontherebetween being that the last two flow channel portions do notcontain transducers therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 schematically illustrates a fossil fuel burning power plant 20utilizing the apparatus and method of the present invention therewithin.Briefly, the power plant 20 has a combustor/burner (furnace) 22, whichis supplied preheated air through inlet duct 24, and fuel through asuitable fuel inlet (not shown). The fuel is combusted with air,producing a flue gas flow 28. The flue gas flow 28 contains NO_(x) andSO_(x) gaseous pollutants, particulate pollutants (sometimes referred toas flyash), and also other combustion products. The flue gas flow heatswater flowing in known boiler tubes (not shown), and converts the waterto steam. The steam is supplied to a suitable turbine/generator (notshown), which produces electric power.

Flue gas flows through the primary flue gas duct 36 and, as shown,through a non-traditional, or “in duct” selective catalytic reduction(SCR) system 38 for the reduction of NO_(x) from the flue gas stream.The flue gas flow 28 then passes through a heat recovery apparatus 40(referred to hereinafter as air preheater 40), wherein heat istransferred to an incoming air flow 42, to provide preheated air flowthrough conduit 24. After leaving the air preheater 40, the gas flow 28enters an electrostatic precipitator 44, in which a large fraction ofthe flyash is removed by application of electrostatic fields to the fluegas passing through the precipitator. Although not illustrated, anotherwell known arrangement for removing particulate from flue gas stream, isa baghouse, wherein the particulate in the flue gas stream passingtherethrough is collected on the surfaces of filter bags containedtherein. The “cleansed” flue gas then flows through an exhaust stack 46for discharge to the atmosphere.

The discussion of the power plant 20 is intended to be highly schematicin nature, and to provide the information and background necessary tounderstand, practice and enable the present invention. In an operatingpower plant, there are typically many other systems, as well asalternative systems, that are not shown here. The present invention iscompatible with such other systems and may, wherever applicable, be usedwith them.

The invention described hereinafter was conceived to overcome thehereinabove mentioned problems and inefficiencies by designing a safe,economical and predictable process for providing a urea to ammoniasystem, generally indicated at 49, when only a small amount of ammoniais required to be produced [i.e. for SCR for small combined cyclesystems or for in-duct catalyst applications (see schematic introductionof ammonia at 50), flue gas conditioning to enhance precipitatorefficiency (see schematic introduction of ammonia at 52) and/oralleviate plume problems, for SNCR applications directly into the boiler22 (see schematic introduction of ammonia at 54, and the like].

System 49 is schematically illustrated in FIG. 1 as comprising: a sourcefor solutionized urea (preferably 15 to 50% urea to water, by weight),shown as storage tank 60; an ultrasonic hydrolysis assembly 64; a pump62 for selective and variable delivery of solutionized urea to assembly64 from tank 60, via conduit 65; and a dilution air subassembly 66 fordiluting the gas stream exiting from the hydrolysis assembly 64, priorto the gas stream, containing gaseous ammonia, is conveyed to itsintended use target (i.e. at injection points 50, 52 and/or 54).Subassembly 64 may be of any known type or configuration and, as shown,comprises: a fan 70 which blows process dilution air through heater 72where it joins with and dilutes (via valved line 74) gaseous ammoniaexiting from assembly 64. As shown the diluted gaseous ammonia streampasses through a gas mixer 76 disposed in conduit 78, which leads to oneor more of the downstream processes which requires gaseous ammonia.

The ultrasonic hydrolysis assembly 64 may take more than one form andpreferred embodiments thereof are illustrated in FIG. 2, FIGS. 3-4, andFIG. 5 as assembly 64′, 64″ and 64′″, respectively.

Exemplary hydrolysis assembly 64′ comprises: an external ultrasonicgenerator 80 electrically connected to a plurality (as shown three)ultrasonic transducers 82 which adapted to be suspended within theultrasonic hydrolysis casing 84 in a manner that the transducers 82 arebelow the normal level 87 of the liquid within the casing 84; a suitableheater 86 (electrical or steam), which is operative to maintain thetemperature of the liquid within the casing 84 at least at or near theboiling point thereof; and a steam sparging assembly 88. A suitable misteliminator 89 is shown adjacent the outlet of assembly 64′ to betterinsure that only a gaseous flow containing ammonia is emitted from theassembly 64′, and that contaminants, if any, from the urea solution arenot carried over from the assembly 64′.

Assembly 64′ is operational as follows:

-   -   1. Solutionized urea is directed to assembly 64′ via conduit 65.        The solution within the assembly 64′ is maintained at a        temperature and pressure of 80 to 150° C. and 1 to 5 bar,        respectively, via any suitable means (i.e. heater 86, preheating        of the solutioinized urea before or during transport to assembly        64′, and/or heat from the steam sparging).    -   2. The ultrasonic generator 80 is energized to cause the        transducers 82 to create a powerful sonic field by emitting        ultrasonic waves, for example in the range of 15 to 100 kHz,        preferably 20 to 40 kHz.    -   3. Creating the ultrasonic waves in the solutionized urea        results in ultrasonic processing which, in turn, results in the        hydrolysis of at least some of the adjacent solutionized urea        into ammonia and carbon dioxide. It is important to note that        this hydrolysis is accomplished while maintaining the static        temperature and pressure of the solution within the hydrolyzer        casing at around 80 to 150° C. and 1-5 bar.    -   4. The sparging assembly 88, which as shown is steam operative,        serves a dual purpose of controlling and increasing the amount        of gaseous ammonia removed from the solutionized urea for use by        downstream processes, and also adding additional heat to the        solutionized urea to assist in making up the loss of temperature        of the urea solution, which resulted from the endothermic        hydrolysis of the urea into ammonia and carbon dioxide.

Exemplary hydrolysis assembly 64″ comprises an external ultrasonicgenerator 90 electrically connected to a plurality (as shown five)elongated ultrasonic transducers 92. The transducers 92, which aretransversely spaced from one another, each have one axial end thereofsupported by the hydrolysis casing 94, intermediate the upper and lowersides of casing 94, and cantilever axially inwardly therefrom. In thisparticular embodiment, two of the transducers 92 have their axial endsupported on one side of the casing 94 and the other three have theirrespective axial ends supported on the opposite side of the casing 94. Acircuitous upwardly open channel 100 is formed within casing 94 and isdefined by spaced channel plates 102 which are disposed between adjacentpairs of transducers 92 and are arranged to provide a circuitous pathfor the solutionized urea from one side of the casing 94 to the other.The upper ends of the plates 102 are free and at an elevation higherthan the operational level 97 of the solution within the casing 94.

Hydrolysis assembly 64″ additionally includes: a plurality (as shownthree) elongated sparging assemblies 98 which are transversely spacedand axially extending in a direction opposite the axis of elongation ofthe transducers 92; a suitable heater assembly 96 for maintaining theselected operational temperature of the solution within the hydrolysisassembly 64″; and a pump (schematically illustrated as 103) forrecirculating the solutionized urea from casing outlet 104 back to thecasing inlet 106 or, in the alternative, back to storage tank 60 foreventual recirculation back to the assembly 64″, or for some other use.

As may be appreciated by one skilled in the art, insofar as the conceptof using high frequency waves to assist in the hydrolysis ofsolutionized urea, is common to both the assembly 64′ and 64″, theassembly 64″ works in much the same manner as the assembly 64′ describedhereinabove, with the primary distinction there between being:

-   -   A. Assembly 64′, as shown, is a “once through” system, whereas,        assembly 64″ is a “re-circulation system”. As is well discussed        in the prior art cited hereinabove, and with particular emphasis        of the applicant's patents, in many instances a recirculation        system has specific advantages over the once through systems.    -   B. Assembly 64″ is more controllable and potentially more        efficient in the time it takes in producing a given quantity of        ammonia.

Hydrolysis assembly 64′″ is similar to hydrolysis assembly 64″ discussedhereinabove and comprises: a hydrolysis casing 124 which is transverselydivided into a ultrasonic section 125 and a sparging and/or evaporatingsection 127; and an external ultrasonic generator 120 electricallyconnected to a plurality (as shown three) elongated ultrasonictransducers 122. The transducers 122, which are transversely spaced fromone another, each have one axial end thereof supported in the ultrasonicsection 125, intermediate the inlet and outlet ends thereof, andcantilever axially inwardly therefrom. In this particular embodiment,two of the transducers 122 have their axial end supported on one side ofsection 125 and the other transducers 122 has its axial end supported onthe opposite side of the section 125. A circuitous upwardly open channel130 is formed within casing 124 and is defined by spaced upwardlyextending channel plates 132, which are arranged to provide a circuitouspath for the solutionized urea from one side of the casing 124 to theother. The plates 132 are transversely spaced within the casing 124. Theupper ends of the plates 132 are unsupported and at an elevation higherthan the operational level of the solution within the casing 124.

The ultrasonic section 125 additionally includes a suitable heaterassembly 136 therewithin for maintaining a selected temperature of thesolution within the section 125. The sparging (nee mechanical agitating)and/or evaporation section 127 includes a plurality (as shown two)elongated sparging assemblies 128 transversely spaced form one anotherand axially extending in second transverse direction opposite such firstmentioned transverse direction, as well as a suitable heater assembly138 for maintaining a selected operational temperature of the solutionwithin the section 25, which may be varied independently of the heater136. A pump (schematically illustrated as 103) for recirculating thesolutionized urea from casing outlet 104 back to the casing inlet 106or, in the alternative, back to storage tank 60 for eventualrecirculation back to the assembly 64″ may also be included.

As may be appreciated by one skilled in the art, the operation ofassembly 64′″ is very similar to the operation of assembly 64″ discussedhereinabove, with the primary exception therebetween being that theprimary evaporation and/or sparging occurs in section 127 and theprimary ultrasonic processing of the urea solution takes place in theultrasonic section 125, making it easier to maximize the efficiency andeffectiveness of the ultrasonic and sparging applications. Furthermore,because sections 125 and 127 have independent heaters the respectivetemperature of the sections can also be optimized for sparging and/orevaporation and ultrasonic applications. For even further effectivenessof the sections 125 and 127, they can be separated from one another in amanner that the section 127 can be independently pressurized from theultrasonic section 125. With such an independent arrangement, a higherpressure can be applied at section 127, than may be desirable ornecessary for the optimal operation of the ultrasonic section 125, forit is known that a relatively higher pressure (i.e. 10 bar or more),coupled with sparging, will yield a greater and/or more controlledcompletion of urea hydrolysis and the release of gaseous ammonia fromthe urea solution.

Inasmuch as the invention herein is primarily directed to the concept ofproducing relatively small quantities of ammonia from a solutionizedfeedstock, on demand and on site, by the use of sonochemistry aidedhydrolysis and, further the nature and operation of ultrasonicgenerators and transducers is well known in the art, further descriptionof sonochemistry and ultrasonic generators thereof is not believed to berequired, and for detailed descriptions thereof, the reader is directedto standard sources for some of such materials to the hereinabovesetforth references and for materials relating to ultrasonic systems andsome typical applications, the reader is directed to: “Ultrasound makesWaves in the CPI”:, Chemical Engineering, August 1999; “Star in a Jar”,Popular Science, December 1998; “News and Notes” Mechanical Engineering,November, 2004; an advertising Brochure of EIMCO Water Technologies,published in 2004 and titled “EIMCO® Sonolyzer™-Sludge Disintegrationand Minimization”; and U.S. Pat. Nos. 5,538,628; 5,372,634 and6,500,219. Furthermore, it is to be understood and appreciated that thedescriptions hereinabove are merely of preferred embodiments of theinvention and further modifications can be made thereto withoutdeparting from the scope of the invention herein, for example: more orless transducers may be provided; although not shown, the generatedammonia may, in instances of small boiler usage, be used for the normalSCR supply, rather than simply in-duct SCR usage; other forms ofphysical agitation may be used for sparging; any suitable transducerdesign may be utilized so long as it is operative to achieve theintended results in hydrolyzation of urea to ammonia in the quantitydesired; if the transducer technology is available and the capital andrunning costs are within permissive competitive parameters, scaled upsystems such as described hereinabove may be used for more conventionalSCR boiler applications; the number and cycling of energized transducersmay be varied, as well as the pulsing and frequencies; evaporation cantake place with or without mechanical agitation (sparging) and/orrecirculation; and the like.

The invention herein shall be defined by the scope and content of theclaims herewith, which include:

1. In an apparatus for the on-site manufacture of a gaseous mixture containing ammonia, from a liquid containing solutionized urea which is hydrolyzed within a chamber, the improvement comprising: at least one ultrasonic processor, in communication with such chamber, and selectively operative to produce high frequency sound which result in portions of such solutionized urea undergoing “cold boiling” to accelerate hydrolysis and produce at least ammonia in such liquid; and means to agitate and/or evaporate portions of such liquid, having undergone cold boiling, to release such gaseous ammonia therefrom.
 2. An apparatus as specified in claim 1 wherein the high frequency sounds produced by such ultrasonic processor are in the range of 15 to 100 kHz.
 3. An apparatus as specified in claim 2 additionally comprising a heating assembly disposed within such chamber and operative therein to maintain the temperature of the solutionized urea within such chamber in the range of 80 to 150° C.
 4. An apparatus as specified in claim 3 wherein said means for agitation includes a steam sparging assembly disposed within such chamber.
 5. An apparatus as specified in claim 1 wherein said ultrasonic processor includes a plurality of ultrasonic transducers adapted to be disposed within such chamber and having the operative parts thereof below the level of such solutionized urea.
 6. An apparatus as specified in claim 5 wherein such chamber is divided into a plurality of parallel upwardly open interconnected channels, and with an ultrasonic transducer disposed within each of such channels.
 7. An apparatus as specified in claim 6 wherein said interconnected channels define a circuitous path from one end such chambers to the other.
 8. An apparatus as specified in claim 2 wherein the high frequency sounds produced by such ultrasonic processor are in the range of 20 to 40 kHz. 